An image projector utilizing a spatial light modulator, such as a digital micromirror device (DMD) or a liquid crystal-on-silicon (LCOS) device, includes an array of pixel light modulator elements which are individually addressable to modulate light according to settings based on image input data for pixel color and intensity. The light modulated by the array elements is projected through optical elements to collectively form an image at a given throw ratio onto an imaging surface, such as a wall, flat surface or screen.
Throw ratio (D/W) is the throw distance (D) from the projector lens to the screen, divided by the width (W) of the projected image. Different lens systems provide different throw ratios. For projectors with zoom lenses, throw ratio may be varied within a given range. However, for projectors with fixed lenses, throw ratio is normally also fixed. To change throw ratio for such projectors, either lens substitutions are made or supplemental lenses are added. For projection over longer distances, such as from the back of an auditorium to a vertical screen on a front wall, projection optics are used that form images with longer throw ratios, e.g., >2.0. If the throw ratio is too short, the projected image may be unclear. For projection over shorter distances, such as for projection from a cell phone, laptop or other portable device onto a horizontal tabletop or nearby wall surface, projection optics are used that form images with shorter throw ratios, e.g., <1.1. If the throw ratio is too long, particularly with microdisplay and portable fixed resolution devices, the image may appear pixelated.